Process of bleaching bast fibers, especially bast fibers of linen, hemp, and the like



rieesoe can-"on or HRHLES Patented Oct. 18, 1932 HELMU'I KORTE, OF FEANKEORT-ON-TI-IE-MAIN, GERMANY, ASSIGNOR TO I. G. FAR BEN- INDUSTRIE AKTIENGESELLSCHAFT, 0F FRANKFORT-ON-THE-MAIN, GERMANY PROCESS OF BLEACI-IING BAST FIBERS, ESPECIALLY EAST FIBERS OF LINEN, HEMP,

AND THE LIKE No Drawing. Application filed March 20, 1930, Serial No. 437,568, and in Germany March 16, 1929.

The present invention relates to improvements in processes for bleaching bast fibers, especially bast fibers of linen, hemp and the like. A full-white can only be obtained by repeated operations with the bleaching met-lb ods hitherto proposed and used in this 1ndustry, which are based upon the comblned efi'ect of successive peroxide and alkaline hypochlorit-e solutions. One is therefore generally contented with obtaining a half or three-fourths white, the yellow tinge, originating as a rule from lignin derivatives, being then removed by subsequent blueing or by subsequently bleaching the goods in the piece to a full-white.

My process differs from the usual processes of bleaching bast fibers in the first place in that the succession of the baths, consisting in employing first peroxide baths and then baths containing hypochlorite compounds, is inverted in th-seeendmalf of the processj and further in that the p -concentrations of the baths containing available chlorine are adjusted to differ from each other, and finally in that a treatment with a liquor of alkaline reaction, for removing lignin substances, is intercalated between the said two treatments by solutions of available chlorine.

More particularly, the invention is carried out substantially as follows:

The bast fibers which need no previous bucking are (first stage) introduced into a hydrogen peroxide solution, which normally is taken from the fifth stage of process and, to make it suitable for use inthe first stage, is

kept at an active oxygen content of about 0.3,

to 1.0 g. per liter and to a soda content of about 6% of the Weight of the goods by the addition of soda ash. If desired, a small quantity of water-glass (1 to 2 grams per liter) may be added but, as a rule, this stabilizing addition may be dispensed with. The goods are preferably kept over night in this bath which is advantageously kept at an elevated temperature up to about 70 G. Then, after rinsing with water, they are transferred to a bath containing l iyp gc hlonous (second stage) which maybe produced in a "or too short a well-known manner by acidulating solutions rather of bleaching powder or sodium hypochlorite, for instance, with hydrochloric acid, or by introducing chlorine into a soda ash solution. Chlorinated water, with or without the addition of a hypo c l i lorite solution, may also be employed for thtparirsse; lliis bleaching bath is rendered ready foruse by adjusting the same to a concentration of 1 to 8 grams of active chlorine per liter and to a hydrogen ion concentration, p 5. The goods are left in this bath for some time at room temperature (the time depending on the quality of the fiber and on the concentration of the active chlorine). After rinsing with water with the addition, if desired, of dechlorinating agents, the goods are steeped (third stage) for about one hour in a hot soda ash solution containing about 2 to Sgrams of soda ash per liter. A sulfite solution or another alkaline means having the same effect may likewise be used instead of the soda ash solution. The solution is then washed off and the goods are (fourth stage) introduced into a second hypochlorite ion containing bath possessing a lower active chlorine concentration, for instance, one half the concentration of the first one, and which, as a rule, is kept slightly alkaline or neutral i. e. adjusted to a hydrogen ion concentration p 7. (Should the bleach, when treating refractory fibers, have advanced too little up to this time, the hypochlorite ion containing bath may be brought to a slightly acid reaction, and then, after its action, it is preferably followed by a treatment with a hot, weak soda ash solution (stage 4a) Then, after rinsing, the second fresh peroxide bath is applied, which has been brought to 0.5 to 1 gram of active oXygen per liter, and to which an addition of about 2 to 3 grams per liter of water-glass has been made. In this bath the goods are left for one half to two hours, the temperatures, being kept within the limits of about 40 to 80 C. The process is completed with the subsequent rinsing operation. Should a slight yellowish tinge remain as a result of too weak solutions having been employed or duration of treatment (in case refractory goods are to be treated), 1

such a tinge may be done away with by repeating the fourth or fifth stage. As a rule, however, when treating normal goods, one days time will sufiice to perform stages one to five.

The several bleaching stages may be carried out, if desired, under elevated or reduced pressure, with stationary or circulating bleaching baths. Of course, the percentage of active oxygen or chlorine in the baths freshly made up depends, to a certain degree, upon the nature of the raw goods. It is preferably ascertained for larger lots of goods by previous experiments.

According to my tests on the Schopper machine, the th regd bleached to full-white by my process has a tensile strength not inferior to that of the raw yarn. With regard to its other properties, it compares favorably in all respects with the products bleached according to the more troublesome and wearisome methods hitherto used. The loss of weight does not surpass the amount which necessarily results from the removal of the coloring contaminations.

I claim:

1. The process of bleaching bast fibers, especially bast fibers of linen, hemp and the like, which comprises subjecting the raw fibers to the following succession of treatments: first a treatment with a hydrogen peroxide solution, then with a solution containing available chlorine and having an acidity corresponding to p 5, then an intermediate soaking in a hot solution of alkaline reaction, then a second treatment with a solution containing available chlorine and showing a reaction corresponding to p 7, and finally again with a solution of hydrogen peroxide, the different stages of the treatment being terminated by rinsing operations.

2. The process of bleaching bast fibers, especially bast fibers of linen, hemp and the like, which comprises subjecting the raw fibers to the following succession of treatments: first a treatment with a hydrogen peroxide solution having an alkaline reaction and kept at an elevated temperature, then with a solution containing available chlorine and having an acidity corresponding to p 5, then an intermediate soaking in a hot solution of alkaline reaction, then a second treatment with a solution containing less available chlorine than in the first treatment, and showing a reaction corresponding to p 7, and finally again with a solution of hydrogen peroxide of alkaline character.

3. The process of bleaching bast fibers, especially bast fibers of linen, hemp and the like, which comprises subjecting the raw fibers to the following succession of treatments: first a treatment with a hydrogen peroXide solution taken from the last stage of the process and made up to a content of about 6 parts of carbonate of soda per 100 parts of the goods to be treated, said solution being kept at an elevated temperature during the treatment, then with a solution containing from 1 to 8 grs. per liter of available chlorine and having an acidity corresponding to p 5, then an intermediate soaking in a hot soda ash solution containing about 2 to 8 grams Na CO- per liter, then a second chlorine treatment with a solution containing 0.5 to 41: grams per liter of available chlorine and showing a reaction corresponding to p 7, and finally again with a solution of hydrogen peroxide containing about 0.4 to 1 gram of active oxygen per liter and showing alkaline reaction by its contents of up to 3 grams of waterglass per liter, said solution being applied while having a temperature from about 40 to 80 C.

4. The process according to claim 3, wherein after the treatment with chlorine in a solution showing a reaction corresponding to p 7 a supplementary chlorine treatment is intercalated, comprising repeating the bleaching steps by acting on the fibers first with an acid chlorine solution and then steeping with a hot soda solution.

In testimony whereof, I aflix my signature.

HELMUT KORTE. 

